The term "jet loom" as used herein refers generally to looms with a fluid driven weft insertion, and specifically, to air jet looms. During the manufacturing of fabrics on jet looms, the loom drive is subject to speed changes. For example, at the start of the loom the speed of the loom drive increases until the specified or rated speed has been reached. Speed changes also occur as intended changes, for example as a programmed speed change required, for example, when various types of threads or rather yarns are being used in the weaving operation. Speed changes are also required when different weaving operations are being carried out. Some yarn types and weaving operations can be performed or implemented only at certain yarn drawing speeds, in order to avoid weft thread breakage and to achieve a high productivity. Examples of such situations are a slow increase in the speed of the loom drive when weaving from a creel beam, in order to accelerate the yarn spools or creels, and speed changes required for certain weaving operations, for example when transitioning from terry weaving to smooth weaving (border weaving) and vice versa.
European Patent Publication EP 0,554,222 B1 discloses a method of controlling the weft insertion in an air jet loom that permits varying the flight time of the weft thread by correspondingly triggering the auxiliary or relay nozzles in order to keep the thread arrival time within a certain time frame. The known method can also be used when the speed of the loom drive is changed in order to maintain a constant weft thread arrival time.
A disadvantage of the above mentioned known method is, for example, that a much higher tension load is exerted on the weft thread when the loom drive shaft rpm is increased, whereby the thread flight time is necessarily shortened. The shortened thread flight time requires an increase in the compressed air supply to the auxiliary nozzles in order to accelerate the weft thread. This increased tension on the weft thread can damage the threads or can lead to weft thread breakage.
European Patent Publication EP 0,501,920 B1 discloses a weft thread insertion control device in air jet looms that determine the optimal time for the weft insertion, for triggering the nozzles, etc., based on values entered into the loom control by the weaver. A disadvantage of the known method is that the basic parameters that depend, among other things, from the speed of the loom drive, the type of the thread used, etc., must be specified or entered by the weaver manually, based on experience or empirical values.